Belt conveyors are commonly used for the transfer of material. The material to be transferred is fed at one end of the belt of the belt conveyor, and when moving forward, the belt transfers the material for the length of the belt conveyor to the other end of the conveyor where the material is discharged from the belt. The lengths of belt conveyors vary according to the required transfer distance of bulk material, ranging from conveyors with a length of less than two meters to conveyors with lengths of even several kilometers.
In certain applications, it is advantageous that the length of the belt conveyor can be made shorter than its working length during its use. For example, during transportation of the belt conveyor from one place to another, it is advantageous that the conveyor can be made shorter to ease the transportation. Particularly when the belt conveyor is connected to a mobile apparatus for the transfer or processing of a material, the possibility of making the belt conveyor shorter is of primary importance, because it enables the flexible transportation of the apparatus to a new location.
Mobile material processing apparatuses are used, for example, for the feeding, transfer, crushing, screening, or washing of mineral materials. Typically, such a processing apparatus comprises a frame and at least one processing unit suitable for the processing of mineral materials, for example a feeder, a belt conveyor, a crusher, a screen, or a corresponding apparatus for transferring, refining or sorting mineral material. Two or more different processing units are often integrated in the same frame to attain an apparatus that is suitable for the versatile processing of mineral material. For the transportation of the apparatus between different working sites or at least within one working site, the frame of the processing apparatus is equipped with runners, wheels or tracks. In many cases, mineral material processing apparatuses are also provided with an independent power source, for example a diesel engine, for moving the apparatus.
There are various solutions of prior art for changing the length of the belt conveyor to the transport position and to the work position again. The essence in these solutions is the method of varying the length of the frame of the belt conveyor. One such solution is to use a telescopic frame construction with pipes which can be placed within each other, so-called slide pipes. The slide pipes have a rectangular cross-section. The frame construction has the shape of a ladder, where the telescopic frame beams of the conveyor consist of slide pipes, between which supporting beams are mounted at both ends at a straight angle to the frame beams. Idlers supporting the conveyor belt from below are mounted on the supporting beams. The shifting of the conveyor to its work position is effected by one or more hydraulic cylinders which are connected, at one end, to the end of the conveyor mounted on the frame of the processing apparatus, and at the other end to the outermost supporting beam of the discharge end of the conveyor. The hydraulic cylinder always extends the conveyor to its full length, and the piston stroke of the cylinder thus determines the length of the conveyor in its work position. In the work position, extended in the full length, the slide pipes carry the weight of the conveyor, and the cylinders take care of the extension of the conveyor. For the tensioning of the conveyor belt, separate belt tensioning means are installed in the frame of the conveyor.
A problem with belt conveyors of the above-described kind is that they are short, having a maximum length of about four meters only. The length of the conveyors is limited by the length and the price of the conveyor extending cylinders.
The frame of the conveyor in mobile mineral material processing apparatuses can also be made of frame blocks connected to each other. Various turning members are installed at the joints. For moving the processing apparatus, the frame blocks of the conveyor are turned to a transport position by means of the turning members.
Document EP 641 607 discloses one such mobile mineral material processing apparatus, in which the belt conveyors which transfer the material from a processing apparatus, for example a screen, and which are, in their work position, extended to the side of the apparatus, are turned onto the top and along the sides of the processing apparatus when the apparatus is prepared for the transport position. For this purpose, the belt conveyor frames are equipped with joints between the frame blocks.
A problem with such turnable belt conveyors is that the preparation of the conveyors to the transport position is cumbersome and time-consuming. Furthermore, in some cases it may require that the operator of the processing apparatus climbs onto the processing apparatus when the conveyor is being turned, which involves the risk of falling of the operator. Another problem is the transport width and height of such processing apparatus and belt conveyors, which may be so great that it is impossible to transfer the combination under narrow transport conditions.
For transferring material, separate conveyor units are also used, which are mobile on transport platforms of their own by means of wheels or rollers, and are provided with belt conveyors intended for the transfer of material only. These conveyor units are moved to the vicinity of the processing apparatus, and they transfer material that comes either directly from the processing apparatus or from a first conveyor arranged in the same frame with the same. Such conveyor units are disclosed, for example, in publications EP 1108661 and WO 99/50091, in which the conveyors can be extended to a work position and shortened for the transport of the conveyor unit. The frame construction of the conveyors is telescopic, wherein for transferring to the transport position, at least a part of the length of the conveyor can be shortened into the structure of the conveyor. The telescopic frame construction of the conveyor consists of a welded and folded profile and has a substantially rectangular cross-section.
These belt conveyors, whose frame construction is made of telescopic parts with a primarily rectangular cross-section, are difficult and expensive to manufacture. The chamfering of the profiles is labour and time consuming. It is particularly cumbersome to manufacture the frame parts sliding in each other with accurate clearances, because in the solutions presented in the prior art publications, the length of the telescopic frame parts is relatively long and the clearances must be held constant over the whole length of the frame part.